NATURAL (RE)COLONISATION 1 – The Seychelles Blue Pigeon

The natural area of occurrence of species is a controversial subject in the local conservation community as it has potentially substantive ramifications for ongoing conservation action plans. In an ideal scenario species would only be introduced (i.e. re-introduced) to islands that they had previously naturally occurred on. The reality however is considerably more complex. The lack of a comprehensive baseline of the original occurrence of species, the dire status and urgent need of many species and the available islands with habitats suitable to support them have required a much more pragmatic approach. These are issues that have been pertinent to the introduction, of the Seychelles warbler, fody and magpie-robin on Denis Island. The pragmatic approach, however, has been prevalent in recent years and continues to improve the status of key rare endemic species.

Not all species require introduction however, man-induced changes to an ecosystem whether they be production landscape changes or attempts at ecosystem restoration create habitats and niches for species that can then establish themselves through “natural” dispersal. A good example of this is the Blue pigeon (Alectroenas pulcherrima) on Denis Island. De Trobriand did not mention any land bird species in 1773 when he first described the island and the pigeon was not recorded in 1907 or 1977 surveys of the island. Today however the blue pigeon is a common sight on Denis with nest building behaviour and juveniles regularly seen. Though no systematic survey of the blue pigeon population on the island has been undertaken a minimum of 23 birds were observed together in a single fig tree in march 2008 and it is estimated that there are at least 50 to 100 birds on the island.

So what has brought about this natural arrival and population growth on the island?
The blue pigeon, an endemic to the Seychelles central archipelago, has an interesting history. It is good to eat and has been heavily exploited in the past with clear evidence of a corresponding reduction in population and range of the species. However a combination of legal protection, public education and improved standards of living has greatly reduced, if not eliminated, this practice and the population has demonstrated rapid growth since the mid 20th century.

Crook (1960) cited the species as “not very rare in these islands”, but this comment was made in the context of endangered birds in the archipelago such as the magpie–robin and warbler which were very rare at that time with global populations of less than 50. Penny (1974) stated that pigeons could still be seen where mountain forest persists, most commonly on Praslin but also in remote parts of Mahe, Silhouette and Fregate. Beamish (1979) noted that numbers seemed to be increasing “particularly on Mahe and also fairly common on Fregate, Silhouette and Praslin.” Skerrett et al (2001) provide considerable information stating that:

• in 1980 the bird was rarely seen below and elevation of 200m but by 2001 it occurred to sea level.
• it was then fairly common on Mahe, Praslin, La Digue and other large wooded granite islands – Curieuse was naturally re-colonised in the 1980s, this being linked to an increase in woodland habitat on the island.
• that it was introduced to cousin in 1990 and that it now breeds there successfully[1].
• Aride Island was naturally re-colonised with the first record in October 1990.

The colonisation of Aride is of particular interest because this is the nearest (56km south) granitic island to Denis and therefore logical source of origin for its population.

Hill (2001) records blue pigeons as present on Denis but does not comment on its relative abundance. This suggests that somewhere between 1990 and 2001 that birds colonised Denis from Aride. This is a very narrow period of time particularly when one would normally assume that the population on Aride would first establish itself and expand to fill the available habitat on the island before emigration to a distant island like Denis would occur.
The current relative abundance of blue pigeons suggests that Denis was colonised shortly after Aride and/or that immigration of birds to the island is ongoing. Denis does appear to be a particularly suitable for Blue pigeons. Even in the mid-20th century when the island’s surface area was dedicated to coconut production visitors noted that an unusual number of broad leaved trees were allowed to flourish within the plantation. The coconut plantations on Denis were abandoned in 1982 and broadleaved trees flourished in the aftermath, developing closed canopies in significant areas of the north east quarter of the island. Today Denis has extensive areas of broadleaved woodland (approximately 50 hectares with another 20 hectares under restoration) including a lot of fig trees, the fruit of which is particularly favoured by blue pigeons. The birds can also be commonly seen feeding on the fruits of the abundant scaevola bushes that fringe the coast of the island. So with abundant food sources on a relatively large predator free island the birds can be expected to prosper.

But should they be there? There are arguments for and against:

• the island is clearly within flying range of the species as proven by the recent natural colonisation of Denis.
• but would the natural vegetation have supported a population of the birds? the original vegetation of Denis consisted of Pisonia dominated broadleaved forest interspersed with grassland areas and the avifauna was dominated by huge sea bird colonies. De Trobriand, the discoverer of Denis certainly doesn’t mention them, but then again his description of the island is limited. Certainly the closely related Comoro blue pigeon has prospered in similar ecosystems.
• the absence of the birds throughout most of the 20th century might be interpreted as meaning the birds were never there but the late 19th and early 20th century saw a diminished population in numbers and range – so if the birds had been extirpated on Denis through human consumption and/or the extensive habitat change on the island during that time, there would have been no ready source of re-colonisation.

There does not currently appear to be any definitive information; and whilst I am personally inclined to believe that Denis does form part of the natural range of the species the population has clearly benefited from the development of man-made secondary habitat on the island.

What can be said, however, is that the blue pigeon is today present and prospering on the island, it is a protected species and a welcome addition to the island’s ecotourism product and current vegetation management regimes mean its population is likely to further expand over the next 5 – 10 years.


[1] From personal observation I can confirm that a breeding population of blue pigeons was established on the neighbouring island of Cousine in the mid-1990’s – nest and juvenile found in 1995.